1. Field of the Invention
The invention is directed to a hydraulic circuit for directing hydraulic fluid to a rotary hydraulic motor. A check valve assembly is positioned between the motor and the control valve for coupling the low pressure supply/return line to reservoir when a direction control valve is in a neutral or checked position.
2. Description of the Prior Art
Hydraulic systems for driving rotary hydraulic motors are well known. In a typical circuit, hydraulic fluid is drawn from a reservoir by a pump and directed to a four-way three-position direction control valve. The direction control valve directs pressurized fluid through one of the supply/return lines to the motor and removes the exhausted fluid from the other supply/return line to the reservoir.
To protect the motor and other hydraulic components, a crossover relief valve system maybe located between the supply/return lines. The crossover relief valve system typically comprises two spring biassed hydraulic pressure relief valves which direct hydraulic fluid from the high pressure supply/return line to the low pressure supply/return line.
When the direction control valve is in a neutral or checked position, hydraulic pressure may build up in the supply/return lines as hydraulic fluid leaks across the direction control valve to the supply/return lines. As the pressure relief in each of these lines dumps to the other line pressure builds up in both lines, overpressurizing the seals of the motor. As such hydraulic fluid may leak through the seals of the motor. Many motors are provided with case drains and case drain lines for directing leaking hydraulic fluid back to the reservoir.
Grapple skidders are forestry work vehicles used to haul logs in rugged terrain. The grapple is located at the rear of the skidder and is used to grab logs. Typically a rotary hydraulic motor is located on top of the log arch for rotating the grapple. This motor is subjected to various loads when the skidder is skidding a log. More specifically, when turning the skidder, the log lags in the turn thereby twisting the grapple and rotating the motor. By twisting the grapple, the logs drive the motor as a pump possibly overloading the crossover relief valves and causing fluid to leak through the seals of the rotary motor. As such the motor must be equipped with a case drain and case drain line.